This invention relates to a process for producing high-density abrasive compacts, in particular high-density diamond impregnated compacts.
A typical fabrication process commonly used in the manufacture of diamond impregnated compacts utilises powder metallurgy (PM) technology, whereby a mixture of diamond grit and bonding powders, predominantly metallic, is consolidated to form a cutting tool. Although hot pressing to net shape has become widespread, the powders can also be densified using other PM processes such as pressure-less sintering or hot isostatic pressing, or a combination of the two, extrusion, laser melting, a combination of hot pressing and laser cutting, and other similar techniques, for example.
The hot pressing process consists of the simultaneous application of heat and pressure so as to obtain a product nearly free from internal porosity. Compared to the conventional cold press/high temperature sintering PM route, hot pressing requires holding the powder for a shorter time (usually 2-6 minutes) at a lower temperature, but under a compressive force, to reach a higher density level. Hot pressing is generally accomplished using resistance heating equipment and graphite moulds. The graphite moulds offer higher efficiency in segment production and, at elevated temperatures, protect both the metal powder and diamond grit against oxidation. Although the use of coated diamond can also offer a certain degree of protection, certain powder mixtures can require temperatures which would considerably damage the diamond during sintering.
A properly densified metal matrix diamond mixture acquires a narrow hardness range which, to a great extent, is affected by the matrix composition. If, however, the structure of the segment deviates substantially in any respect, or if the densification is incomplete, the hardness does not fall within the specified range. Incompletely densified materials usually have extremely low toughness, which may result in poor wear resistance and poor diamond retention.